Gaseous discharge tube control system

ABSTRACT

A control system for gaseous-discharge tubes which operates upon the hysteresis characteristic of a gaseous-discharge tube. A voltage V1 is normally applied to one electrode of the gaseousdischarge tube, whereas two voltages V2 and V3 are applied to the other electrode through a resistor and a diode respectively. The gaseous-discharge tube is turned on only when the junctions at which said voltages V2 and V3 are impressed, are grounded in response to the driving pulses. The gaseous-discharge tube remains turned on even after the driving pulses have disappeared.

United States Patent [none 1 Sept. 4, 1973 I GASEOUS-DISCHARGE TUBE CONTROL 3,614,739 10/1971 Johnson 315/169 TV SYSTEM 3,618,071 11/1971 Johnson et al.... 315/166 X 3,686,661 8/1972 Sharpless .1 315/169 TV [75] Inventor: Takashi lnoue, Asaka, Japan [73] Assignee: Ricoh Co. Ltd., Tokyo, Japan Primary Ex m n R0y Lake Assistant Examiner-Hugh D. Jaeger [22] May 1972 AnorneyHenry T. Burke et al. [21] App]. No.: 256,373

[57] ABSTRACT [30] Foreign Application Priority Data A control system for gaseous-discharge tubes which op- June 5, 1971 Japan 46/39552 erates p the yst r sis ha acteristic of a gaseousdischarge tube. A voltage V is normally applied to one [52] US, Cl 315/169 TV, 315/166, 315/169 R electrode of the gaseous-discharge tube, whereas two 315/172 voltages V and V are applied to the other electrode [51] Int. Cl. H0515 37/00, H05b 39/00 through a resistor and a diode respectively The g [58] Field 61 Search 315/136, 165, 166, ens-discharge tube is turned on y when thejunetiens 315/169 R 169 TV 172 at which said voltages V and V are impressed, are

grounded in response to the driving pulses. The gase- [56] Reference Cited ous-discharge tube remains turned on even after the driving pulses have disappeared.

3 Claims, 4 Drawing Figures GASEOUS-DISCHARGE TUBE CONTROL SYSTEM BACKGROUND AND SUMMARY OF THE INVENTION:

The present invention relates to a control system for gaseous-discharge tubes, and more particularly an ON- OFF control system for an array of gaseous-discharge tubes such as neon glow lamps used as a display device for an electronic computer, an analyzer or the like.

In general, electronic computers, analyzers or the like are provided with display devices for representing the processed data for immediate use. Various display elements such as gaseous-discharge tubes, photodiodes, liquid crystal, EL (electric luminescence) elements, cathode ray tubes and the like are widely used, but the gaseous-discharge tubes such as neon glow lamps find a wide application because their operation is stable and dependable and the cost is low.

In general, a gaseous-discharge tube is fired or turned on at a starting voltage different from a voltage at which the gaseous-discharge tube is extinguished or turned off. The starting voltage or turn-on voltage V, is higher than the turn-off voltage V,,. Therefore, when a pulse voltage which is higher than the difference between the starting voltage V, and a bias voltage V intermediate the voltages V,, and V, normally impressed to a gaseous-discharge tube is impressed or superposed upon the bias voltage V,, the gaseous-discharge tube is immediately turned on, and remains turned on even after the pulse voltage has disappeared. To turn off the gaseous-discharge tube, a negative pulse voltage which is less than the difference between the bias voltage V and the tum-off voltage V,, may be applied only for a very short time.

In the discharge-tube display devices, a large number of gaseous-discharge tubes such as neon glow lamps are arrayed in rows and columns. To operate the gaseousdischarge tube display device, there has been used a control system which works on the hysteresis characteristic of the gaseous-discharge tubes used for statically controlling the ON-OFF controls of selected gaseous-discharge tubes. That is, each of the gaseousdischarge tubes arrayed in rows and columns is impressed with a bias voltage V,., and the driving pulses are impressed or superimposed on the bias boltage V, of a selected gaseous-discharge tube through a row and column driving circuits external of the array of gaseous-discharge tubes so that the sum of the bias voltage V, and the pulse voltages may be over the starting or tum-on voltage V,. As a result, the selected gaseousdischarge tube is turned on, and remains turned on even after the pulse voltages have disappeared.

However, in the control system of the type described, the pulse driving voltages are also impressed on all gaseous-discharge tubes in the selected row and column so that they tend to be turned on very often. To overcome this probelm, there has been proposed a control system in which each gaseous-discharge tube is provided with an AND circuit which outputs the signal only when the row and column driving pulse voltages are simultaneously applied so that in response to the output signal from the AND gate, only the selected gaseous-discharge tube may be turned on. In this control system, the AND gates will not output the signals when only the row or column driving pulse voltage is applied so that the erratic operation resulting when gaseous-discharge tubes that are not selected are fired Another object of the present invention is to provide a control system for an array of gaseous-discharge tubes in which each gaseous-discharge tube is provided with a special AND circuit designed in accordance with the present invention so that a reduction in the number of circuit component parts may be attained.

Briefly stated, according to the present invention, one electrode of the gaseous-discharge tube is connected to a first power source, whereas the other electrode is grounded through a series circuit comprising a current limiting resistor and a first resistor. The junction between the current limiting resistor and the first transistor is connected to a second power source, and the junction between the other electrode of the gaseous-discharge tube and the current limiting resistor is connected through a diode to a third power source which in turn is grounded through a second transistor. When both the first and second transistors are cut off, the voltage which equals the difference between the voltages of the first and second power sources is impressed to the gaseous-discharge tube so that the latter remains turned off. However, when both the first and second transistors are conducting, the voltage impressed to the gaseous-discharge tube rises to the voltage of the first power source so that the gaseousdischarge tube is turned on. Once the gaseousdischarge tube is turned on, it remains turned on even fter the first and second transistors are both cut off.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a graph of the voltage-current characteristic curve of a gaseous-discharge tube for explanation of the hysteresis characteristic thereof;

FIG. 2 is a circuit diagram of one prior art ON-OFF control system for gaseous-discharge tubes;

FIG. 3 is a circuit diagram used for explanation of the underlying principle of the present invention; and

FIG. 4 is a circuit diagram of a control system for an array of gaseous-discharge tubes in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows the voltage-current characteristic curve of a typical gaseous-discharge tube (to be referred to as a discharge tube" for brevity in this specification). The voltage applied to the discharge tube is plotted along the abscissa whereas the current flows through the discharge tube along the ordinate. It is seen that the starting voltage or tum-on voltage V, is different from the tum-off voltage V,,. That is V, V,,. Therefore, when the bias voltage V, intermediate the tum-on and turn-off voltages V, and V, is normally impressed to the discharge tube, the latter will be immediately turned on when a pulse voltage which is equal to the difference between the starting voltage V and the bias voltage V is superposed upon the bias voltage V ONce the discharge tube is turned on, it remains glowing even if the pulse voltage is removed. In like manner, when the negative pulse voltage which equals the difference between the bias voltage V and the tum-off voltage V, is impressed, the discharge tube may be immediately turned off.

When the hysteresis characteristic of the discharge tube described above is utilized, one or any number of plurality of discharge tubes may be selectively turned on or turned off.

Next referring to FIG. 2, the prior art display device will be described briefly in order to clearly point out the problems encountered in the prior art device. The display device is shown as comprising a 2 X 2 array of the discharge tubes T T T and T but it should be understood that in practice a large number of discharge tubes are used. One electrode of the discharge tube T is connected to a first d-c power source V whereas the other electrode is grounded through a current limiting resistor R and a transistor Tr The junction between the current limiting resistor R and the transistor Tr is connected through a resistor to a second d-c power source V To the base of the transistor Tr is connected an AND circuit comprising diodes D D and D To thejunction a between the diodes D and D is impressed through a resistor a positive voltage V The instantaneous positive pulse signals P and Q are applied to the diodes D and D Other discharge tubes T T and T are connected in a similar manner to that described above. The voltage V of the first d-c power source is the starting or turnon voltage V and the difference between the voltages V and V of the first and second d-c power sources is the bias voltage V When the pulse signals P and Q are both absent, the potential at the junction a is almost zero so that the transistor Tr remains cut off. As a result, the bias voltage (V V is impressed to the discharge tube T so that the latter remains turned off. When either of the pulse signal P, or Q is applied to the diode D or D the potential at the junction a is still zero so that the transistor Tr still remains cut off. As a result, the discharge lamp T still remains turned off. When both the pulse signals P, and Q are applied to the diodes D and D,,', the potential at the junction a rises to V 7 which is applied through the diode D to' the base of the transistor Tr so that the latter is conducted. As a result, the voltage impressed to the discharge tube T rises to the voltage V of the first d-c power source, that is the starting voltage V so that the discharge tube T is now turned on. Even if both the pulse signals P and Q, disappear so that the transistor Tr is cut off, the discharge tube T remains turned on. The other discharge tubes T T and T are turned on in a manner similar to that described above.

The diode D is inserted in order to prevent the transistor Tr from conducting in response only to either of the pulse signals P, or Q, so that this diode D cannot be eliminated in the prior art device. As a result, each discharge tube unit requires three diodes and one transistor so that the circuitry becomes complex in con struction and expensive in cost with the increased number of circuit component parts.

THE PRESENT INVENTION Next referring to FIG. 3, the underlying principle of the present invention will be described. One electrode of the discharge tube T is connected to the power source with the voltage V whereas the other electrode, that is the junction 0 is grounded through a current limiting resistor R and a transistor Tr, The junction d between the resistor R and the transistor Tr is applied with the voltage V through a resistor R and the junction 0 between the discharge tube T and the resistor R is applied with the voltage V; through a diode D and a resistor R the junction e between which is grounded through a transistor Tr To the bases of the transistors Tr and Tr, are applied the instantaneous pulse signals P and Q, respectively so that the transistors Tr and Tr: are conducted or ON. The magnitudes of the voltages V V and V are so selected as to satisfy the following condition:

where V starting or turn-on voltage; and V, turn-off voltage. More preferably the voltages V, and V; are so selected that when the discharge tube T is turned off, the potential at the junction c equals the voltage V When both the transistors Tr and Tr are cut off, the potential at the junction 0 is given by the following relation: Potential at c V (R R g/(R R R R a u) where R,,= internal resistance of diode D. It is seen that in order that the second term of Eq. (1) may become zero,

when the transistor Tr, is conducted whereas the transistor Tr, is cut off, the potential at the junction 0 is given by Potential at c od/( os R: ROI) a Since it is preferable that the potential at the junction 0 equals the voltage V the following relation must be satisfied: I

From Eqs. (2) and (4), the voltages V and V, must be ideally so selected as to satisfy the following relation:

When the voltages V, and V, will not satisfy Eq. (5), the bais voltage impressed to the discharge tube T is decreased so that the erratic operation tends to occur very often. I

When the transistors Tr and Tr, are both cut off, the potential at the junction c equals the voltage V: so that the voltage (V, V,) is impressed to the discharge tube T. As a result, the discharge tube T remains turned off. When the transistor Tr, is conducting whereas the transistor Tr, is cut off, the potential at the junction e lowers to the earth potential, but the potential at the junction 0 remains at the level of the voltage V, because the current which flows from the power source V, through the resistor R and R,,, to the junction e is interrupted by the diode D. As a result, the discharge tube T remains turned off.

Next when the transistor Tr, is conducting and the transistor Tr, is cut off, the potential at the junction d is at the earth potential so that the current from the power source with the voltage V, flows into the transistor Tr, through the resistor R the diode D and the resistor R,,,. In this case, the potential at the junction 0 is given by Eq. (3), and the voltage equal to V, R,,,/(R,,, R, R,,,) V, is impressed to the discharge tube T. However, the current limiting resistor R,,, is relatively very high so that R,,, R,,,, R,

Therefore, the voltage impressed to the discharge tube T is slightly higher than the voltage V, V,,) so that the discharge tube T remains turned off.

Next when the transistors Tr, and Tr, are both conducting in response to the pulse signals, the potentials at the junctions c and d are equal to the earth voltage so that the voltage V, is impressed to the discharge tube T. As a result, the discharge tube T is turned on. Once the discharge tube T is turned on, it remains turned on even when the transistors Tr, and Tr, are both out off because the voltage (V, V is impressed to the discharge tube T.

In summary, according to the present invention, only when the pulse signals P and Q are simultaneously applied to the transistors Tr, and Tr, so that the latter are caused to conduct simultaneously, the discharge tube T is turned on. However, when only one of the signal pulses P and Q is applied, the discharge tube T will not turn on.

In FIG. 4, the embodiment of the prsent invention is shown as comprising a 2 X 2 array of discharge tubes T,,, T,,, T,, and T,,, but it should be understood that in practice a large number of discharge tubes are arrayed. Since the circuit arrangements of the four discharge tube units are substantially similar it will suffice to describe only one unit T,,. The voltage V,, is impressed to one electrode of the discharge tube T,,, and the other electrode is grounded through the resistor R,, and the transistor Tr,,. The voltage V,, is impressed through the resistor R, and the diode D,, to one end of the resistor R,,, and the voltage V,, is impressed through the resistor R, to the other end of the resistor R,,. The junction between the resistor R, and the diode D,, is grounded through the transistor Tr,,. It should be noted that the transistor Tr, is common to the discharge tubes T,, and T,, whereas the transistor Tr,,, common to the discharge tubes T,, and T,,. Similarly, the transistor Tr,, is common to the discharge tubes T,, and T,, whereas the transistor Tr,,, common to the discharge tubes T,, and T,,. That is, only one transistor is provided for the discharge tubes in each row and column, and only one diode D is provided for each discharge tube.

The voltages and circuit component parts shown in FIG. 4 correspond to those shown in FIG. 3 in the following manner. That is, the voltage V,,, V,, and V,, correspond to the voltage V,, V, and V,, respectively;

the resistors R,,, R, and R,, to the resistors R R and R respectively; the transistors Tr,, and Tr,,, to the transistors Tr, and Tr,, respectively; and the diode D,,, to the diode D. The voltages V,,, V,, and V,, are selected .to satisfy the relations described with reference to FIG. 3.

When the pulse signals P, and 0, (corresponding to the pulse signals P and Q in FIG. 3) are applied to the bases of the transistors Tr,, and Tr,,, respectively, the latter are caused to conduct so that the discharge tube T,, is turned on. In like manner, only when the pulse signals P, and Q, are applied simultaneously, the discharge tube T,, is turned on. Only when the pulse signals P, and Q, are applied simultaneously, the discharge tube T,, is turned on. Only when the pulse sig nals P, and Q, are simultaneously applied, the discharge tube T,, is turned on. Once the discharge tube is turned on, it remains turned on even after the pulse signals P and Q have disappeared. To turn off the discharge tube T,,, the impression of the voltage V,, is ceased.

What is claimed is:

l. A control system for a gaseous-discharge tube comprising a. a gaseous-discharte tube having two electrodes b. means for impressing a voltage V, to one electrode of said gaseous-discharge tube,

c. means for impressing a voltage V, to the other electrode of said gaseous-discharge tube through a resistor,

d. means for impressing a voltage V, to said other electrode of said gaseous-discharge tube through a diode, and

e. means for grounding the points at which said voltages V, and V, are applied only when a selected pair of driving pulses are applied to the means for grounding, said voltages V, V,, and V, satisfying the following relation where V, starting or tum-on voltage of the gaseous discharge tube, and V, turn-off voltage of the gaseous discharge tube. I

2. A control system for a gaseous-discharge tube as set forth in claim 1 wherein said point at which said voltage V, is applied is grounded through a first switching element which in turn is driven by a first driving pulse and whose state is reversed in response to said first driving pulse; said point at which said voltage V, is applied is grounded through a second switching element which in turn is driven by a second driving pulse, whereby only when said first and second pulses are simultaneously applied to said first and second switching elements said voltage application points are grounded to thereby turn on the gaseous-discharge tube.

3. A control system for an array of a plurality of gaseous-discharge tubes comprising a. a plurality of gaseous-discharge tubes arrayed in rows and columns, b. means for impressing a voltage V, to one electrode of each of said plurality of gaseous-discharge tubes, c. means for impressing a voltage V, to the other electrode of each gaseous-discharge tube through a resistor,

d. means for impressing a voltage V to the other relation:

electrode of each gaseous-discharge tube through a diode V1 V V1 V; V e. means for grounding all points in one row at which Vl V y Va Vb said voltage V, is applied only when a row driving pulse is applied to said one row, and

f. means for grounding all points in one column at where which said voltage V is applied only when a 001- I: Stamng tum-011 g and umn driving pulse is applied to said one column, V tum-Off voltage.

said voltages V V and V satisfying the following 10 

1. A control system for a gaseous-discharge tube comprising a. a gaseous-discharte tube having two electrodes , b. means for impressing a voltage V1 to one electrode of said gaseous-discharge tube, c. means for impressing a voltage V2 to the other electrode of said gaseous-discharge tube through a resistor, d. means for impressing a voltage V3 to said other electrode of said gaseous-discharge tube through a diode, and e. means for grounding the points at which said voltages V2 and V3 are applied only when a selected pair of driving pulses are applied to the means for grounding, said voltages V1 , V2, and V3 satisfying the following relation V1 > Va > V1 - V2 > Vb V1 > Va > V1 - V3 > Vb where Va starting or turn-on voltage of the gaseous discharge tube, and Vb turn-off voltage of the gaseous discharge tube.
 2. A control system for a gaseous-discharge tube as set forth in claim 1 wherein said point at which said voltage V2 is applied is grounded through a first switching element which in turn is driven by a first driving pulse and whose state is reversed in response to said first driving pulse; said point at which said voltage V3 is applied is grounded through a second switching element which in turn is driven by a second driving pulse, whereby only when said first and second pulses are simultaneously applied to said first and second switching elements said voltage application points are grounded to thereby turn on the gaseous-discharge tube.
 3. A control system for an array of a plurality of gaseous-discharge tubes comprising a. a plurality of gaseous-discharge tubes arrayed in rows and columns, b. means for impressing a voltage V1 to one electrode of each of said plurality of gaseous-discharge tubes, c. means for impressing a voltage V2 to the other electrode of each gaseous-discharge tube through a resistor, d. means for impressing a voltage V3 to the other electrode of each gaseous-discharge tube through a diode, e. means for grounding all points in one row at which said voltage V2 is applied only when a row driving pulse is applied to said one row, and f. means for grounding all points in one column at which said voltage V3 is applied only when a column driving pulse is applied to Said one column, said voltages V1, V2 and V3 satisfying the following relation: V1 > Va > V1 - V2 > Vb V1 > Va > V1 - V3 > Vb where Va starting or turn-on voltage, and Vb turn-off voltage. 